Sounds like the overvoltage relay is working correctly!
There are 4 sensor imputs to the fuel computer that must be correct for the car to idle correctly. Those imputs would need to be checked when the car is idling too high!
MERCEDES Benz Master Guild Technician (6 TIMES)
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44 years foreign automotive repair
27 Years M.B. Shop foreman (dealer)
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190E 2.3 16V ITS SCCA race car (sold)
1986 190E 2.3 16V 2.5 (sold)